The manufacture of ophthalmic compensation spectacles is based on operations for taking ophthalmic measurements, to determine the values of spherical and/or cylindrical compensation of each eye of a user, as well as on measurements of physiological parameters, such as the monocular pupillary distances, necessary for correct positioning in terms of centering and orientation of the lenses with respect to a spectacle frame.
In the case of the manufacture of progressive lenses, a near vision zone and a far vision zone are furthermore determined for each lens.
Depending on the selected spectacle frame, the optician determines the diameter of the lenses that is suitable for the shape of the outline of the rims of the frame.
The determination of the diameter of the lenses for a spectacle frame may present difficulties on account of a wrap angle of the spectacle frame, i.e. of a general curvature of the frame in the Fraunhofer plane of the user or on account of a dihedral angle of the frame, that is to say of an angle between the respective holding planes of the right and left lenses in the frame. The determination of the diameter of the lenses for a spectacle frame may be further complicated by taking the camber of the lenses into account, that is to say the interior and/or exterior curvature of the ophthalmic compensation lenses.
Ophthalmic compensation lenses are generally provided with erasable markings corresponding to the optical center in far vision (in general a fitting cross), to a reference line indicating the axis of the cylinder (referenced by dashes), in case of cylindrical correction, and, to a near vision zone, in case of progressive lens (in general a small circle).
After mounting the lenses in the frame, it is desirable to verify the proper positioning of the lenses with respect to the frame. For progressive spectacles, it is moreover desirable to verify the location of the near vision and far vision zones, with or without the erasable markings. This check can be performed with or without the user, but it is desirable to show the user the result of this check so as to alert him to the importance of a mounting suited to his morphology and to his vision.
Patent document FR 2578660 describes an apparatus for determining the diameter of the uncut ophthalmic lenses to be fitted in a determined spectacle frame. An apparatus of this type is illustrated in FIG. 1. This type of apparatus is based on the use of printed charts. Each printed chart 15 comprises a plurality of plots corresponding to uncut ophthalmic lenses of different peripheral diameters. The apparatus 10 comprises a plinth 11, a curved chart guide 14 for inserting a printed chart 15, a support 12 specific to the fitting of the spectacle frame 5 to be equipped and an arm 13 movable in translation for holding the spectacle frame in the support 12. This apparatus 10 allows the diameter of the ophthalmic lenses to be determined before mounting. When the curve of the chart guide 14 corresponds to the wrap of the spectacle frame 5, this apparatus 10 makes it possible to reduce the parallax between the spectacle frame 5 and the printed chart 1. However, the wrap of the chart guide 14 does not always correspond to the wrap of the spectacle frame 5, thus resulting in parallax errors. Moreover, a preprinted chart in general represents a plurality of concentric rims, which may be difficult to distinguish, thus giving rise to errors in reading the diameter of the rims of the frame.
Patent document US 2012/0073153 describes another instrument for measuring the diameter of lenses for a spectacle frame, comprising a chart holder of concave shape, a slider making it possible to insert a flexible printed chart into the chart holder and a spectacle frame support. The instrument is provided with a series of preprinted charts representing most lenses as a function of their diameter, outline shape, etc. To measure the diameter of the lenses, the wrapped face of convex shape of a spectacle frame is placed against a printed chart inserted into the concave chart holder. In an advantageous manner, the chart holder comprises several slits, each slit allowing the printed chart to be curved according to a predetermined radius of curvature, so as to fit the wrap of the flexible printed chart to suit the wrap of the frame. This instrument makes it possible to determine the diameter of the lenses intended to be mounted on a spectacle frame before the spectacles are manufactured. This instrument also allows a final verification of the mounting of the lenses on the frame.
However, the prior art apparatuses require a complete series of preprinted charts corresponding to the various diameters and shapes of lenses. Now, the number of frames and of shapes of available lenses multiplies the number of necessary charts. The optician does not always have preprinted charts corresponding to all the available lenses.
Moreover, the prior art apparatuses do not make it possible to check certain mounting parameters, such as the position of the vision zone as a function of the spectacle wearer's pupillary distance. Accordingly, complementary measurements are generally used, for example via another measurement instrument equipped with a video camera. The optician generally acquires a first image of the wearer wearing the spectacle frame before the lenses have been mounted, and then a second image of the wearer wearing the spectacle frame after the lenses have been mounted.
Thus, FIG. 2 shows a first image 50 of a user wearing a demonstration spectacle frame, furnished with lenses with no marking and no optical power, for the measurement of the user's physiological parameters. In FIG. 2, the user looks straight ahead, in far vision. The measurement instrument makes it possible, by known techniques, to determine in the first image 50: the center of the pupil 53 of the right eye in far vision, referenced by a cross, and the near vision zone 55 of the right eye, referenced by a circle with respect to the image of the right rim 51 of the frame. Likewise, the following are determined with respect to the image of the left rim 52 of the frame: the center of the pupil 54 of the left eye in far vision, referenced by a cross, and the near vision zone 56 of the left eye, referenced by a circle. The XY plane of FIG. 2 is referenced in an XYZ orthonormal coordinate system, the X axis passing through the centers of the pupils 53, 54 of the two eyes. By calibration, the image 50 of FIG. 2 makes it possible to measure for example the inter-pupillary distance or the mounting height of a progressive lens with respect to the lower edge of the rim of the frame.
FIG. 3 shows a second image 60 of a user wearing the same spectacle frame as in FIG. 2, after mounting of progressive lenses 61, 62. Various reference markers appear on the lenses: centering reference markers (centering crosses 63, 64), markers indicating the far vision zones (discontinuous circles 73, 74), markers indicating the near vision zones (continuous circles 65, 66), and horizontal lines 67, 68, 69, 70. The image 60 of FIG. 3 makes it possible to check the mounting of the lenses in the spectacle frame worn by the user. The image 60 of FIG. 3 makes it possible to verify that the edging, the centering and the positioning of the lenses are correct or to detect possible centering and/or mounting errors.
In the case where the mounting of the lenses is satisfactory, the image 60 allows the optician to show the user that the selection of the lenses and their mounting are suited to the personalized vision of this user. The physical reference markers, in general temporary markings 63-71, are then erased by the optician.
In case of defective mounting, the optician performs the necessary modification, and then in general undertakes a new checking step, through a new image acquisition of the wearer with the spectacle frame after correction of the mounting of the lenses. However, these steps of successive checks are time-consuming for the wearer and the optician.
One of the objectives of the invention is to propose an apparatus and a method for determining the diameter of a spectacle lens that is easily configurable for a spectacle frame as a function of the diameter and of the shape of the available lenses.
Another objective of the invention is to propose an apparatus and a method for checking the mounting of a lens on a frame, not requiring the presence of the spectacle wearer.